The present invention relates, in general, to vacuum-coating and in particular to a new and useful vapor coating device in which the carrier of the vapor-emitting material is constructed so as to be rotatable and driven by a motor by means of a transmission mechanism.
Vapor sources, for which the carrier of the vapor-emitting material, for example, a melting crucible for the material to be vaporized, is constructed so as to rotate are known. The German Auslegeschrift No. 1,521,525, for example, shows how to make a vaporizing crucible rotate for the purpose of holding the molten, vaporizable material by centrifugal force on the interior of the vaporizing crucible. The surface of the melt attain a desired shape due to the centrifugal force, and focussing of the vaporized particles is possible. Also, the distribution of the vapor, condensing the substrate, can be influenced. It is a further advantage that, due to the paraboloid shape of the surface of the melt bath as the crucible is rotating, the surface area and, with it, the emission of vapor is increased.
It has also already been proposed to influence the distribution of the coating material through the choice of the rotational speed of a vaporizing crucible, this process offering the advantage that the distribution curve can be altered and adapted to particular conditions by changing the rotational speed even during the vapor-coating process itself.
A further advantage with rotatable crucibles is described in the German Offenlegungschrift No. 3,316,554. In this arrangement, the crucibles are combined with a crucible-changing device and the crucible, which is in the vaporizing position, can be caused to rotate by a shaft connected to it. Vaporizing installations, with a device for rotating the material to be vaporized during the vaporizing process, are also described in the British Patent No. 1,318,046, the German Offenlegungsschrift No. 3,010,925 and the German Offenlegungsschrift No. 2,616,215. For the arrangement described in the last-mentioned reference, the material to be vaporized can additionally be moved in the vertical direction of the axis of rotation, that is, its height can be adjusted.
For all the arrangements mentioned, the motor was usually arranged outside of the vaporizing chamber and the rotational motion was introduced into the vacuum by means of a sealed shaft. Because the shaft was passed through the wall, the vaporizer itself was fixed in the vacuum chamber, with the exception that the height could be adjusted.
FIG. 7 of German Auslegeschrift No. 1,521,525, however, shows the possibility of making the rotary transmission lead through in a tiltable fashion, so that the shaft can be tilted to extend in different directions, adaptable to the respective requirements.
A rotatable vaporizer, which can be adjsuted in the lateral direction (perpendicular to the axis of rotation), has become known from the German Patent No. 2,849,933. The three most important components of an electron beam vaporizing device, namely the holder for the material to be vaporized, for example, a vaporizing crucible, an electron beam source and a deflecting magnet for the electron beam being mounted on a common holding rod and the holding device for the material to be vaporized being constructed as a rotating crucible with a motor, which is mounted on the same holding rod and operated in the vacuum chamber. The holding rod itself is passed vacuum-tightly through the wall of the vacuum chamber and could be moved for a suitable adjustment.
In the electronics industry, thin metal layers are frequently applied with electron beam vaporizers in the production of microswitch circuits. Electron beam vaporizers are also frequently used for the production of optical layers. For these applications, the requirements, which the vaporizing equipment must meet, are very high. In particular, exceptionally high requirements are with respect to the homogenity of the layer thickness distribution, the layer thickness reproducibility, the adherence of the vapor to a particular angular distribution, etc. The highest requirements can be fulfilled only if:
(a) the material is always vaporized from the same source location within the vaporizing chamber, the location being accurately defined, and PA1 (b) the characteristics of the dispersion of the vapor are as constant as possible.
It is well known that rotating or moving the material to be vaporized under the electron beam produces a significantly smoother vapor-deposition behavior. For low-melting metals, such as, for example, aluminum, the splash frequency is drastically reduced thereby and bath oscillations, which lead to fluctuations in the vapor dispersal are also significantly reduced. For high-melting metals, the development of holes and craters in the vaporized material, which also have a disadvantageous effect on the vapor dispersion, is avoided by rotating the crucible. For dielectrics, such as, for example, silica, or for subliming materials such as chromium, the "burning in" of holes is prevented, once again, by rotating the crucible. With this method, even large surfaces of material can be vaporized very evenly and uniformly. It is also more readily possible to keep the source location stable and small by means of the rotation; for crucibles of large diameter, this cannot be achieved with the help of beam scanning alone (wobbling).
The best results are, however, achieved when rotation and a programmed beam deflection are used together. The beam deflection then serves only for the purpose of defining an exact vaporizing zone over a small, precise region.
The rotating-crucible vaporizers, used until now, were quite expensive to operate. The driving mechanisms were in each case arranged outside of the vacuum chamber, where they were frequently in the way. The leadthroughs, required for the driving mechanism, also place an appreciable limit on possible installations. The site of the vaporization could therefore be selected only within certain limits.
The problems mentioned are particularly serious when several layers must be applied in a single vapor-deposition process, which very frequently is the case these days. Until now, one has made do with so-called multi-hole crucibles. With such a system, the individual crucible cups can be brought consecutively into the vaporization position. This type of source permits vaporization from always the same site; however, it does not solve the problems of uniform vaporization, because there is no rotation of the crucible cups about their own axis.